Cob: windows

[Darel Henman]

Jen,
 Here are some numbers for you to bounce around.

jen walker wrote:
> I've been warned that the seal on an old
> double glazed window may not be up to snuff and you might end up with
> windows fogging over once installed.

Single pane windows fog over just as well.  If there's a rend in the
seal put some sealant on it.  I'd slide in a little desicant bag first
then seal it.

> What I'm getting to is that this friend learned from the
> window dealer that even the best double windows only have an R value of three
> whereas a single pane has about an R value of one. Not that great a
> difference. 

It is a great difference.  Its triple a single panes value.  It would
let 1/3 less heat out through the window.  Do your math.

Example: if you had a 3 x 3 ft window (= 9 ft^2) and the ouside temp is
30 deg_f and inside is 70 degF, then the differences of heat lost is
below for R-val= 3 and R-val = 1.

R-value of 3:
	(24 hrs * (inside_temp_F - outside_temp_F)*square_foot_of_window) /
R-Value = btus lost in a day
	(24 h * (70 F - 30 F) * 9 ft^2 ) / 3 hr per ft^2 per deg_F / btu
         8640 / 3 = 2,880 btus

R-value of 1:
	(24 hrs * (inside_temp_F - outside_temp_F)*square_foot_of_window) /
R-Value = btus lost in a day
	(24 h * (70 F - 30 F) * 9 ft^2 ) / 1 hr per ft^2 per deg_F / btu
         8640 / 1 = 8640 btus

Over a months period the different is say 30 days * (8640 -2880) or
172,800 btus of heat lost more through a single pane window.  This one
window only heat loss difference can be made up for with 1.81 gallons of
propane gas.  If you have 3 cold months then triple this to 5.43 gallons
of propane gas.  This is for only one small 3 ft by 3 ft window.

Now if you have more than one window you have to add the losses there. 
And if you use the house more than one winter you have to multiple that
times the number of years your losing heat.  Then multiple by the cost
of the propane and you'll get an idea of live cycle costs.


Darel



I was wondering, since single panes would be easier to
> salvage
> or make etc. if any of you out there know if they'd be o.k. in very
> cold
> winters with of course heavy curtains after the solar gain from them
> was
> done for the day. Perhaps they'd get too frosty.
> thanks,
> Jen Walker